3 research outputs found
Surfactant phosphatidylcholine metabolism in preterm infants studied with stable isotopes
AIM OF THE STUDIES
1. To develop and use a novel method to study surfactant metabolism in preterm and older
infants.
(chapters 3 and 4).
2. To study endogenous surfactant synthesis in relation to prenatal glucocorticosteroids.
(chapters 5 and 6).
3. To study the influence of surfactant therapy on endogenous surfactant metabolism.
(chapters 7 and 8).
4. To study surfactant composition and concentration after surfactant therapy.
(chapter 8)
Metabolism of endogenous surfactant in premature baboons and effect of prenatal corticosteroids
We studied the synthesis of surfactant and the effect of prenatal
betamethasone treatment in vivo in very preterm baboons. Ten pregnant
baboons were randomized to receive either betamethasone (beta) or saline
(control) 48 and 24 h before preterm delivery. The newborn baboons were
intubated, treated with surfactant, and ventilated for 6 d. They received
a 24-h infusion with the stable isotope [U-(13)C]glucose as precursor for
the synthesis of palmitic acid in surfactant phosphatidylcholine (PC).
Palmitic acid in surfactant PC became enriched 27 +/- 2 h after the start
of the isotope infusion and was maximally enriched at 100 +/- 4 h. The
fractional synthesis rate of PC palmitate in the beta group (1.5 +/-
0.2%/d) was increased by 129% above control (0.7 +/- 0.1%/d) (p < 0.02,
Mann- Whitney U test). The absolute synthesis rate of PC in the beta group
[1.6 +/- 0.3 micromol/kg/d] was increased by 128% above controls [0.7 +/-
0.2 micromol/kg/d] (p < 0.02). These data show that the synthesis of
endogenous surfactant from plasma glucose as precursor is a slow process.
It is shown, for the first time in vivo, that prenatal
glucocorticosteroids stimulate the synthesis of surfactant PC in the very
premature baboon
Endogenous surfactant turnover in preterm infants measured with stable isotopes
We studied surfactant synthesis and turnover in vivo in preterm infants
using the stable isotope [U-13C]glucose, as a precursor for the synthesis
of palmitic acid in surfactant phosphatidylcholine (PC). Six preterm
infants (birth weight, 916 +/- 244 g; gestational age, 27.7 +/- 1.7 wk)
received a 24-h [U-13C]glucose infusion on the first day of life. The
13C-enrichment of palmitic acid in surfactant PC, obtained from tracheal
aspirates, was measured by gas chromatography-combustion interface-isotope
ratio mass spectrometry. We observed a significant incorporation of
carbon-13 from glucose into surfactant PC palmitate. PC palmitate became
enriched after 19.4 +/- 2.3 (16.5 to 22.3) h and reached maximum
enrichment at 70 +/- 18 (48 to 96) h after the start of the label
infusion. The fractional synthesis rate (FSR) of surfactant PC palmitate
from glucose was 2.7 +/- 1.3%/d. We calculated the absolute production
rate of surfactant PC to be 4.2 mg/kg/d, and the half-life to be 113 +/-
25 (87 to 144) h. Data on endogenous surfactant production and turnover
were obtained for the first time in human infants with the use of stable
isotopes. This novel and safe method could be applied to address many
important issues concerning surfactant metabolism in preterm infants,
children, and adults